1. Field of the Invention
The invention relates to a process for joining the heating rod of a glow plug to a glow plug body.
2. Description of the Prior Art
Joining the heating rod of a glow plug to its glow plug body by pressing the heating rod into the body was known beforehand. To do this a hydraulic pressing means is used which produces a central force fit between the heating rod and the body. Conventionally, the heating rod is pressed axially from the combustion space-side glow plug tip into the glow plug body. The axial force on the tip of the heating rod necessary to do this is highly dependent on the tolerances of the hole in the body and the heating rod diameter as well as the respective surface composition. Since the amount of projection of the heating rod from the glow plug body is an important parameter of the function of the glow plug in installation and engine operation, the press path during installation must be monitored; due to the high pressing force especially in thin and comparatively long heating rods there is the danger of damage of the heating rod by buckling, tilting, striation and deformation so that the pressing force may not exceed the predetermined maximum value. Therefore, the pressing force must also be monitored during the pressing process.
Monitoring of the force-path is technically complex, the long pressing path, associated with the high pressing forces, entailing the enumerated risks; for coated heating rods in addition the coating is destroyed.
The indicated defects of the known production process occur increasingly as glow plugs become smaller with respect to the diameter of their heating rod and glow plugs become longer overall; this in turn promotes construction of space-saving engines. Likewise, one possible new process will enable smaller deviations from concentricity; similarly the process will also be usable for coated heating rods.
A primary object in accordance with the present invention is achieved by the process of joining the heating rod of a glow plug to its glow plug body in which a centered force fit between the heating rod and the glow plug body is produced by the radial force acting on the glow plug body.